Objective: To examine the effects of cigarette smoking, giving up smoking, and primary or secondary pipe or cigar smoking on the risk of type 2 diabetes.
Research design and methods: A prospective study followed 7,735 men aged 40-59 years from general practices in 24 British towns for an average of 16.8 years. Incident cases of physician-diagnosed diabetes were ascertained by repeated postal questionnaires and systematic reviews of primary care records.
Results: A total of 290 incident cases of diabetes were found in 7,124 men with no history of diabetes, coronary heart disease, or stroke. Cigarette smoking was associated with a significant increase in risk of diabetes, even after adjustment for age, BMI, and other potential confounders. The benefit of giving up smoking was only apparent after 5 years of smoking cessation, and risk reverted to that of never-smokers only after 20 years. The risk of diabetes in those who switched from smoking cigarettes to pipe or cigars remained equal to the risk in continuing cigarette smokers. Men who gave up smoking during the first 5 years of follow-up showed significant weight gain and subsequently higher risk of diabetes than continuing smokers.
Conclusions: Cigarette smoking is an independent and modifiable risk factor for type 2 diabetes. Smoking cessation is associated with weight gain and a subsequent increase in risk of diabetes, but in the long term, the benefits of giving up smoking outweigh the adverse effects of early weight gain.